Method for reducing the sulfur tri-oxide content of combustion gases resulting from the combustion of spent pulping liquors

ABSTRACT

IMPROVED COMBUSTION OF SPENT LIQUORS FROM THE SULFITE AND SULFATE CELLULOSE PROCESSES RESULTING IN A SIGNIFICANT DECREASE OF SO3 CONTENT IN THE FLUE GASES FROM THE COMBUSTION IS OBTAINED BY MIXING THE SPENT LIQUORS WITH A COMPOUND OF A GROUP IIA ELEMENT WITH THE EXCEPTION OF BERYLLIUM AND RADIUM SUCH AS A MIXTURE OF A METAL SALT AND A METAL SOAP, PARTICULARLY MAGNESIUM SULFATE AND MAGNESIUM TALL OIL FATTY ACID SOAP. THE SPENT LIQUORS CONTAINING GROUP IIA COMPOUNDS, THE ALKALINE EARTH METAL COMPOUNDS, CAN THEN BE COMBUSTED.

United States Patent Office 3,745,064 Patented July 10, 1973 3,745,064 METHOD FOR REDUCING THE SULFUR TlRl- OXIDE CONTENT OF COMBUSTION GASES RESULTING FROM THE COMBUSTIQN F SPENT PULPING LIQUORS Axel Mentor Isaksson, Arjang, Sweden, assignor to Bycosin AB, Karlstad, Sweden No Drawing. Continuation-impart of abandoned appliea= tion Ser. No. 717,980, Apr. 1, 1968. This application Dec. 28, 1970, Ser. No. 102,066

Int. Cl. D2lc 11/12 US. Cl. 162-30 9 (Ilaims ABSTRACT OF THE DISCLQSURE Improved combustion of spent liquors from the sulfite and sulfate cellulose processes resulting in a significant decrease of 80;, content in the flue gases from the combustion is obtained by mixing the spent liquors with a compound of a Group lIla element with the exception of beryllium and radium such as a mixture of a metal salt and a metal soap, particularly magnesium sulfate and magnesium tall oil fatty acid soap. The spent liquors containing Group Ila compounds, the alkaline earth metal compounds, can then be combusted.

This application is a continuation-in-part of copending application Ser. No. 717,980, filed Apr. 1, 1968, now abandoned.

This invention relates to a method for significantly reducing the amount of sulfur trioxide produced during the combustion of waste off-lye liquors from the sulfite and sulfate cellulose processes. It has been common practice to dispose of the spent liquor by releasing it to nearby streams and other water bodies causing severe water pollution in many instances. The spent liquors can be combusted; however, the combustion gases contain sulfur trioxide which again is a severe pollutant when released into the atmosphere. In addition the sulfur trioxide condenses with water forming sulfuric acid which is highly corrosive on the metal dues of the combustion equipment.

The present invention provides a combustion process for disposing of Waste off-lye liquors which avoids the pollution and corrosion problems of the prior art processes as mentioned above by significantly reducing the sulfur trioxide content of the combustion gases by controlling in advance the composition of waste liquor being burned. To this end, the present invention provides a combustion process wherein a composition, comprising a compound of a Group Ila element with the exception of beryllium and radium, an alkaline earth metal compound, is added to the waste off-lye liquor prior to the combustion thereof. The composition containing the' Group Ila metal compound is preferably added to the off-lye Liquor or mixtures of off-lye liquor and fuel oil immediately before combustion. Alternatively, however, the additive composition can be mixed with the process stream in an early stage of production of pulp from cellulose, e.g. at the knot obtainer or strainer, whereupon the off-lye waste from the pulping process can be burned directly.

The waste off-lye liquors containing the additive composition can be burned as the sole fuel source for the combustion process or alternatively, fuel oil can be mixed with the off-lye liquors containing the additive composition and the mixtures used as the fuel source for the combustion process.

The additive composition comprises a Group II a metal compound of magnesium, calcium, strontium and barium. The additive composition preferably comprises a mixture of an alkaline earth metal salt and an alkaline earth metal soap. The metal salt and metal soap are mixed in proportions between 9:1 and 1:9 and preferably 3:6 to 6:3 with a particularly suitable proportion being 2:1. The fatty acid in the metal soap contains 2 to 20 carbon atoms and particularly preefrred fatty acids are the tall oil fatty acids. A particularly preferred additive composition comprises magnesium sulfate as the metal salt and magnesium tall oil fatty acid in the metal soap.

Thus, a preferred embodiment of the process according to the present invention is accomplished by mixing magnesium sulfate and a magnesium fatty acid soap with the waste off-lye liquor prior to the combustion of the off-lye liquor. The fatty acid is preferably a tall oil fatty acid. The magnesium sulfate is dissolved in water. The magnesium sulfate solution is then added to an emulsion or solution of magnesium soap. The magnesium sulfate, magnesium soap solution is then added to the waste olflye liquor prior to combustion.

The metal salt, metal soap composition is added to the off-lye waste liquor in proportions ranging from 15% by weight to by weight. The Waste off-lye liquor can then be directly combusted or mixed With fuel oil and then combusted. It has also been found that adding a small amount of magnesium oxide to the combustion air inhibits corrosion caused by the combustion gases.

Monoethanol amine can be added to the metal salt, metal soap solution to neutralize the solution.

The present process will be more fully described by reference to the following example.

EXAMPLE Magnesium, tall oil soap (10 kg.) and MgSOA, (15 kg.) was added to liters of waste sulfite lye. The lye was then combusted in a furnace. The combustion gases contained up to 85% less S0 than combustion gases obtained when sulfite lye to which no additive had been added was burned.

The off-lyes from the sulfite or sulfate cellulose processes can also be processed according to this invention by adding MgSO; and magnesium soap to the off-lye solution (the off-lye solution usually contains about 45% water and 55% lignin) and then evaporating the solution where upon the concentrated off-lyes are burned. The off-lye solutions containing the magnesium additives can also be evaporated to dryness and the solids remaining then burned.

What is claimed is:

ii. In a process for burning waste off-lyes from the sulfite or sulfate industry, the improvement comprising adding to said olf-lyes, prior to burning, (l) a salt of an alkaline earth metal selected from the group consisting of magnesium, barium, strontium and calcium and (2) a fatty acid metal soap, said fatty acid containing from 2 to 20 carbon atoms and said metal selected from the group consisting of magnesium, barium, strontium and cal cium, the total of (l) and (2) added to said waste offlyes being from about l585% by weight of said otf-lyes and the proportion of metal salt to fatty acid metal soap being 9:1 to 1:9, whereby the S0 content of the combustion products is greatly reduced.

2. A process as claimed is claim 1 wherein the waste off-lyes containing the alkaline earth metal salts of (l) and the fatty acid metal soap of (2) are mixed with fuel oil prior to the combustion step.

3. A process as claimed in claim ll wherein the metal salt is magnesium sulfate.

3. A process as claimed in claim 1 wherein the fatty acid metal soap is magnesium tall oil fatty acid soap.

5. A process as claimed in claim 1 wherein the metal 6. A process as claimed in claim 1 wherein monoeth-" anolamine is added to the waste off-lyes prior to combustion.

7. A process as claimed in claim 1 wherein the proportion is 2:1.

8. In a process for burning waste olf-lyes from the sulfite or sulfite industry, the improvement comprising adding to said olf-lyes, prior to burning, (1) magnesium sulfate and (2) magnesium tall oil fatty acid soap, wherein the proportion of ofi-lyes to magnesium sulfate to magnesium tall oil fatty acid soap is about 10:1.5 :1, the total of (1) and (2) being from 15-85% by weight of said ofi-lyes, whereby the S0 content of the combustion products is greatly reduced.

9. A process as claimed in claim 8 wherein the waste olf-lyes are mixed with fuel oil prior to the combustion step.

References Cited UNITED STATES PATENTS Murdock 23 -4s Cann l62-36 Harding 162-30 X Drew 162-29 X Guerrieri 2348 Olson 16'236 Stevens 44,-51

Cann 162--30 Tomlinson 16236 US. Cl. X.R. 

